Process for pressure-forming metallic bodies



3,349,4- 72 PROCESS FOR PRESSURE-FORMING METALLIC BODIES Filed Sept. 15,1956 Oct. 31, 1967 w. SCHLEGEL 5 Sheets-Sheet 1 /NI/EN70P WERNERSCHLEGEL AGENT 3,349,472 PROCESS FOR PRESSURE-FORMING METALLIC BODIESFiled SEPT. 15, 1966 Oct. 31, 1967 w. SCHLEGEL 3 Sheets-Sheet 2 m I I.v/////// a? .ll A

/N VEN70,Q WERNER SCHLEGEL B1 A? Al I 1967 w. SCHLEGEL 3,349,472

, Filed Sept. 15, 1966 PROCESS FOR' PRESSURE-FORMING METALLIC BODIES v.5 Sheets-Sheet 3 /NVN729/P WERNER SCHLEGEL -,p3' BY 3 AGENT UnitedStates Patent ()fifice 3,349,472 PROCESS FOR PRESSURE-FORMING METALLICBODIES Werner Schlegel, Camphausenstrasse 2, Dusseldorf, Germany FiledSept. 15, 1966, Ser. No. 621,718 Claims priority, application Germany,Feb. 27, 1962,

Sch 31,051; Oct. 9, 1965, Sch 37,851

7 Claims. (Cl. 29-528) This application is a continuation-in-part of mycopending application Ser. No. 574,467, filed Aug. 23, 1966, andoriginally entitled, Process for Forging and Pressure- FinishingCast-Metal Alloys,

In the aforementioned copending application, I describe a process and anapparatus for forging and pressurefinishing cast-metal bodies having acrystal transformation or recrystallization point at an elevatedtemperature below the melting or solidification point of the metal andambient or room temperature. This process and system was particularlyapplicable to cast-metal alloys such as steels and cast irons which,after being cast in molds, were cooled to the forging temperature andthen shaped under pressure to their final configuration.

In accordance with the improved method of my earlier application, themolten metal is cooled from the liquid or casting state in a castingmold to the transition temperature or range of temperatures at which atransformation of the crystal lattice takes place from thehightemperature form to the low-temperature form, the pressure finishingbeing carried out without passing below this temperature. The improvedsystem derives in part from the fact that cast iron and most commonmetal alloys have a very high compressive strength but only limitedtensile strength; hence these metals are comparatively brittle. Withcast iron, it is the graphite or free-carbon content which is apparentlyresponsible in large measure for the brittleness. In fact, the highcompressive strength is a consequence of crystal strain developed in thesolidified structure; this strain arises because the secondary graphite,which precipitates out within the transition or transformationtemperature range of 906 to 721 C. (for cast iron), occupies from threeto four times more volume than an iron crystal or grain. By carrying thepressure forming the body in the manner indicated above, the crystalstructure is permitted to homogenize and equilibrate in thermodynamicrespects so that the grains, crystals or atoms of the body are able toreorient themselves without leaving behind significant stress. Inparticular, the lamella separation of secondary graphite (in cast iron)is minimized so that a uniform stress distribution, which contributessignificantly to raising the tensile strength, can result. In thatapplication I point out further that the molds filled with molten metalshould be conveyed to a soaking furnace or pit or to a homogenizationoven whose temperature corresponds to the transition range of the alloyand thence to the forging press at the rate at which the latter canprocess the bodies. In this manner, a highly eflicient plant operationis obtainable.

Moreover, it was also demonstrated that the cast shapes of theworkpieces (i.e. the preforms) should have essentially the same volumeas the final shapes but with a difference in surface area. It was thusemphasized that, in accordance with the improved process, theexpenditure of work and energy in pressure finishing the bodies, couldbe considerably reduced if the hot-working of the cast piece takes placeat high press temperatures without going below the transitiontemperature range; the forging is advantageously combined with apressure finishing or polishing. Accordingly, the cast shapes orpreforms constituting the workpieces to be subjected to pressurefinishing have a smaller surface area than the final shapes 3,349,472Patented Oct. 31, 1967 emerging from the presses. The smaller surfacearea of the cast preform is determined by planimetric analysis for eachcross-section of the finished workpiece, thereby establishing thesmallest surface area or circumference applicable to each cross-sectionof the final workpiece. This method is simple to carry out and permitsof designing the molds accurately to the corresponding requirements.

I have now found that essentially similar methods can solve a problemcharacteristic of nonalloyed relatively pure metals and especially theso-called light metals such as aluminum. Pure metals, especiallyaluminum, which are to be cast from the liquid state, are characterizedby a unique physical property which renders them diflicult to handle.These pure metals (pure here referring to the lack of alloyingingredients) are found often to be highly viscous in the liquid state sothat they tend to fill the casting molds rather poorly and leave voidsor unfilled portions, especially when complex shapes are involved. Forthis reason, the metallurgical field has generally avoided castingtechniques when using such metals or has resorted to alloying to modifythe physical properties of the metal. Indeed, aluminum alloys tend to bemore fiowable and less viscous than pure molten aluminum and such alloysfrequently have an increased strength. However, alloying involvesnumerous disadvantages which are also significant. Thus, alloyingingredients increase the resistance of a cast body to forging andpressure deformation, give rise to internal or intercrystallinecorrosion as a consequence of potential differences Within the crystallattice, alter the characteristic electrode potential of the ,body, andmodify deleteriously the creep resistance and "aging characteristicsthereof.

It is, therefore, the principal object of the present invention toprovide an improved process for the shaping of pure metals as well as ofmetal alloys, which are to be initially cast, and thereby to extend theprinciples originally set forth in my copending application mentionedabove.

A more specific object of the present invention is to provide a methodof and an apparatus for the shaping of metals while eliminating theaforementioned disadvantages.

In accordance with the present invention, the pure metal is cast in amold from a melt and cooled below the critical recrystallizationtemperature and pressure formed in a shaping press, the mold cavity andthe cast preform having the same volume as the pressed finished body buta smaller surface area than the latter. With respect to the surface-arearelationship of the preform and the finished body, at identical volumes,the method for cast-metal alloys is the same as that for pure metals ornonalloyed castings.

The invention is based in part upon the recognition that pure metalsalmost invariably pass through a recrystallization phase. Thus, inaccordance with this aspect of the invention, it may be stated thatrecrystallization phenomena are observed in metals or alloys which arebrought to elevated temperatures. Upon such an increase in temperature,structural changes take place in the metallic body which significantlyand disadvantageously effect the strength characteristics thereof. Theserecrystallization phenomena occur only above a critical temperaturewhich is dependent upon the material, ie the pure metal. In accordancewith the invention, this metal-dependent parameter is ascertained foreach metal to be shaped and the casting thereof is cooled below thecritical recrystallization temperature prior to mechanical shapeningunder pressure. The pressure shaping of the preform or casting iscarried out without altering the volume of the workpiece, whileincreasing its surface area whereby the surface area of the preform isless than that of the finished body. This characteristic of the presentinvention may be summarized succinctly as the increasing of the specificsurface area of the body by mechanical working; for the presentpurposes, the specific surface area will be defined as the ratio ofexternal surface area to volume of the workpiece. In this manner, onlythe surface zones of the crystal structure are subjected to adeformation under pressure. It has been found to be importantsubstantially uniformly to deform the body over its entire periphery orcircumference so that uniform stresses are applied to the lattice andundesirable structural changes are avoided. By maintaining therelationship of surface areas of the preform and the finished body (andtherefore the casting cavity and the forging space) in the mannerpreviously indicated, I have found that the deformation of the bodyoccurs substantially only along surface zones thereof with greater easethan has been possible heretofore. It appears that these surface zonesof the preform are forced into the free spaces of the forging cavitywith a creeping deformation of the metal grains or crystal structureonly in these surface regions with a flow of metal which does notrequire the considerable stresses and forces hitherto necessary forforging metallic bodies. It can be established, therefore, that thisimproved deformation and mechanical working of the body yields anincrease in the specific gravity thereof.

In the case of relatively pure metals, which are cooled in accordancewith the present invention below the crystal transformation point priorto mechanical working, the metal body possesses a fine-grain orsmall-crystal structure characteristic of high strength.

Furthermore, the rapid reduction of the temperature of the body to alevel beneath the recrystallization temperature, is usually carried outas rapidly as possible so that the recrystallization characteristic ofstabilization at this level cannot result. Crystal growth is therebyprevented and only a negligible reduction in strength, by virtue of thecooling action, can be observed. Another advantage of the presentinvention is that the finished nonalloyed body has a completely smoothsurface and indeed, in the case of aluminum, a silver-like mirrorfinish. By comparison, aluminum alloys of the type used commonlyheretofore have grayish-blue coloration and are not significantlycorrosion-resistant.

In both cases (ie for metal alloys such as steels and cast iron and forpure metals such as aluminum) the final deformation is carried out in ahot-forming press or forge with a predetermined capacity in terms ofnumbers of articles to be processed per unit time. Cast-iron bodies(e.g. those having a carbon content generally ranging between 2 and 4%)are treated after casting in a soaking furnace advantageously held at atemperature in the recrystallization zone (say 910 C. to 720 C. for theironbearing material). This soaking furnace or homogenizing oven can, ingeneral terms, be considered to have a temperature of slightly above thecritical recrystallization temperature and at least the lower limitthereof. The preforms are thus fed to the mold from the soaking furnaceat a rate determined by the press capacity. In the case of pure aluminumbodies, the homogenization furnace is maintained at a temperatureslightly below the critical recrystallization temperature and the bodiesare supplied to the hot-forming press in accordance with its capacity. Ahomogenization furnace has the important advantage that the workpiecescan be deformed at elevated temperatures (which correspond to or arebelow the recrystallization temperature as the case may be) withoutrequiring reheating of the bodies. It is also possible, however, to coolpure-aluminum workpieces, after casting, to room temperature and then todeform them in the cold state in so-called cold-forging apparatus. Alsoin this case it is possible to obtain a fine-grained crystal structurehaving high strength.

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1a is an elevational view of a plant for the casting, finishing andforging of metal objects in accordance with the present invention;

FIG. lb is a plan view thereof;

FIG. 2 is a side-elevational view, partly in section, of the castingmold, showing means for severing extraneous material from the castingbody;

FIG. 3a shows plan and side-elevational views of a preformed workpieceto be forged, in accordance with the invention, with the cross-sectionsAK thereof taken along the lines A-A through K-K.

FIG. 3b shows plan and side elevational views of the metal body afterforging wit-h corresponding cross-sections AK taken along the lines AA'through K'--K, respectively; and

FIG. 4 is a cross-sectional view through the forging devicediagrammatically showing the forging plunger or ram.

The device shown in FIGS. 1 and 2 consists principally of a graphite-rod(e.g. are or resistance-heating) furnace 1, in which smelting occurs. Abucket 1', shiftable along the arm 1" of a crane 1a, serves to supplythe raw material to the furnace. The melt 2 is transferred in batches toa crucible 2, from which it is dipped by a workman and poured intoclosed bipartite molds 4 disposed on a tumtable 3. At a dischargestation D, diametrically opposite the pouring station P, the molds 4 areopened and the preformed workpieces or blanks of solid metal are fedinto a soaking furnace 5, the temperature of which corresponds to theaforementioned transition range of the alloy or a temperature well belowthe transition range for pure metals; this range generally can bedetermined from the phase diagram of the alloy and lies between the Aand A oc/'y transformation temperatures (for iron). A workman removesthe preformed workpieces from the soaking furnace 5 and conveys them tothe forging press 6.

The casting arrangement can naturally also be a sandcasting arrangement,known per se, although turntables with split permanent molds arepreferred. As FIG. 2 shows, the molds 4 arranged on the turntable 3 eachconsist of two mold halves 7 and 8. Mold half 7 is movable by pneumaticor hydraulic means 9, so that it is closed against the other mold halfand juxtaposed therewith in the casting zone P, but is opened uponapproaching the soaking furnace 5, so that the casting can be extractedfrom the mold. For this purpose there are associated with the moldhalves 7, 8 ejector pins 10, normally held out of the mold cavity bysprings 10, which, on opening of the mold, strike with their rearwardends against an abutment 12; the latter arrests the pins 10, so that onfurther relative displacement of the mold halves away from each otherthey eject the castings, which then fall onto a conveyor belt or thelike, schematically shown at 10", disposed beneath the mold, whence theycan be conveyed automatically to the soaking furnaces. The furnace maylikewise be provided with a conveyor for continuously carrying thebodies therethrough.

To cut off the pouring heads, vent risers and other excess, a device isprovided which comprises a cut-off plunger 13. The plunger 13 has anaperture 16, normally registering with the pouring spout 16' of themold, and is displaceable by pneumatic or hydraulic means 14 throughaligned slots 15, 17, in the mold halves 7 and 8 so that the riserprojecting through the opening 16 is sheared off upon actuation ofcylinder 14. The means 9 for closing and opening the mold halves 7, 8 aswell as the pneumatic or hydraulic means 14 for the cut-off plunger arecontrolled in accordance with the rotation of the mold turntable 3.

In FIG. 3, there is shown in comparison with one another the preferredworkpiece 19 and the finished body 20 after forging of a door handle,with their associated cross-sections. In accordance with thecorresponding finished article 20, the preformed workpiece or casting 19receives a smaller surface area by approximate formation of the mold.This smaller surface area for the cast (i.e. preformed) shape of theworkpiece 19 is fixed by planimetric determination of the smallestperipheral distance or circumference applicable to the correspondingcrosssectional area of the finished article 20.

The plunger 18 of the forging press 6 shown diagrammatically in FIG. 4illustrates clearly how a plunger can be stepped in such manner that thedeforming forces are transmitted through the steps of the workpiece tobe deformed. Thus there are no tapered pressing surfaces provided on theplunger, but step-like sections 18a-18d, which successively engage theworkpiece 6 held by the anvil 6" of press 6, and exert a shearing actionthereon while effecting a creeping displacement of material in thedirection of arrows 21, 22 while the main component of the press force(arrow 23) is transformed into a downwardly and inwardly acting force(arrow 24) against the reaction forces (arrows 25). Thus there is almostno material removal and only a reshaping of the body from its castconfiguration into the desired one. The steps of plunger or ram 18 willof course be designed to suit the particular conditions.

It will be apparent that many modifications are possible within thespirit and scope of the invention claimed. Thus for example there existsthe possibility or mechan-izing the transfer of the hot workpieces fromthe mold tumtable to the soaking furnace and from the latter to theforging press. Additionally, the turntable 3 may synchronize theoperation of the power means 14, which activates the shearing member 13,and the drive means 9 for the mold members via a microswitch 28, thelatter being tripped at the discharge station D to energize theelectromagnetic valves 29 and 30 associated with these means. Anotherswitch 31 is energized at the casting station P to close the molds andrestore the shearing member 13 to its original position.

While the apparatus has been described above in conjunction with theformation of a cast-iron body whose transition or transformation rangeof 906 C. to 721 C. is not passed during the cooling of the body andwhich is worked at this temperature, it will be understood that theidentical considerations except for the temperature conditions will beinvolved in the formation of a purealu-minum body or any other so-calledlight metal of pure (nonalloy) state. Thus the recrystallizationtemperature of pure aluminum is approximately 470 C. and thecastaluminum bodies are cooled rapidly therebelow. I have discoveredthat the bodies are best worked after they have been cooled to a levelof 150 C. to 250 C. and then worked at this temperature. The soaking orhomogenization furnace 5 of the apparatus would, in this case, bemaintained at a temperature between 150 C. and 250 C. For other puremetals, transition temperatures are available from the literature andphase diagrams and the forging temperatures will be selectedaccordingly.

The invention described and illustrated is believed to admit of manymodifications within the ability of persons skilled in the art, all suchmodifications being considered within the spirit and scope of theappended claims.

I claim:

1. A method of producing bodies from a metal having a crystaltransformation between a high-temperature form and a low-temperatureform, comprising the steps of casting the metal in a liquid state in amold; solidifying the metallic body thus produced and cooling it to aforging temperature in the temperature range at which saidtransformation takes place; and forging said body after said coolingthereof, the configuration of said body generally approaching theconfiguration of the object to be produced, said body having a volumesubstantially identical with said object but a surface area differenttherefrom, said body being reshaped upon forging to conform to thecontours of said object, said method further comprising the steps ofplanimetrically determining the minimum circumferential distanceassociated with each cross-section of said object and forming said moldwith a configuration in accordance with the planimet-rically determinedminimum surface area of the volume of said object.

2. A method as defined in claim 1 wherein said body is brought to saidforging temperature upon removal from said mold in a soaking furnace foruniformly heating said body and is forged immediately after removal fromsaid soaking furnace.

3. A method as defined in claim 1 wherein said mold is formed with acavity and a pouring spout communicating with said cavity, furthercomprising the step of shearing excessive metal from said body at atemperature within said range prior to forging.

4. A method as defined in claim 1 wherein the forging of said body iscarried out by subjecting said body to contact with a stepped ram havingportions successively engageable with said body for deforming it with ashearing action adapted to shape said body without substantial removalof material.

5. A method as defined in claim 1 wherein said metal is an iron-bearingmetallic material and said temperature range is between substantially910 C. and 720 C., said forging being carried out without cooling belowsaid range.

6. A method as defined in claim 1 wherein said metal is nonalloyed andsaid forging is carried out at a temperature below said range.

7. A method defined in claim 6 wherein said metal is aluminum and theforging is carried out at a temperature of substantially to 250 C.

References Cited UNITED STATES PATENTS 356,974 2/ 1887 Bagaley 29-5282,246,886 6/1941 Kroll 1482 2,310,703 2/1943 McGleney 148-2 2,871,557 2/1959 Tarmann et a1. 29528 2,995,816 8/ 1961 Ma 2.9--528 JOHN F.CAMPBELL, Primary Examiner.

-P. M. COHEN, Assistant Examiner.

1. A METHOD OF PRODUCING BODIES FROM A METAL HAVING A CRYSTAL TRANSFORMATION BETWEEN A HIGH-TEMPERATURE FORM AND A LOW-TEMPERATURE FORM, COMPRISING THE STEPS OF CASTING THE METAL IN A LIQUID STATE IN A MOLD; SOLIDIFYING THE METALLIC BODY THUS PRODUCED AND COOLING IT TO A FORGING TEMPERATURE IN THE TEMPERATURE RANGE AT WHICH SAID TRANSFORMATION TAKES PLACE; AND FORGING SAID BODY AFTER SAID COOLING THEREOF, THE CONFIGURATION OF SAID BODY GENERALLY APPROACHING THE CONFIGURATION OF THE OBJECT TO BE PRODUCED, SAID BODY HAVING A VOLUME SUBSTANTIALLY IDENTICAL WITH SAID OBJECT BUT A SURFACE AREA DIFFERENT THEREFROM, SAID BODY BEING RESHAPED UPON FORGING TO CONFORM TO THE CONTOURS OF SAID OBJECT, SAID METHOD FURTHER COMPRISING THE STEPS OF PLANIMETRICALLY DETERMINING THE MINIMUM CIRCUMFERENTIAL DISTANCE ASSOCIATED WITH EACH CROSS-SECTION OF SAID OBJECT AND FORMING SAID MOLD WITH A CONFIGURATION IN ACCORDANCE WITH THE PLANIMETRICALLY DETERMINED MINIMUM SURFACE AREA OF THE VOLUME OF SAID OBJECT. 